The so-called appearance method refers to the conditions that must be met for special NPCs to manifest in front of others.
For instance, the Treasure Mermaid's appearance condition is: Gathering Land.
As long as a civilized Gathering Land appears, the Treasure Mermaid will open a pool nearby, serving as the entrance and exit to the instance.
Rabbit Town conveniently meets this condition, hence the pool connecting Silver Coral Island appeared.
Previously, Angel only knew the appearance condition of the Treasure Mermaid, but now through further search of authority, he learned about the appearance conditions of the "Rainbow Sprite."
—Gathering Land and Rainbow.
Like the Treasure Mermaid, one of the prerequisite conditions for the Rainbow Sprite's appearance is Gathering Land; in addition, there needs to be a rainbow across the sky above the Gathering Land.
To put it more vividly: in a town full of humans, a rainbow appears over the sky.
